Released in 1981 — as the name suggests — the ZX81 was designed to be a cheaper and slightly improved version of Sinclair’s first computer, the ZX80. It proved to be a very popular low-cost computer in the UK. Like its predecessor, it was based on the Z80 microprocessor, and available ready-made or in kit form — I remember seeing regular adverts for it in electronics magazines.
In order to meet the low price point, the ZX81 had quite a limited specification. It had no colour, no sound, a membrane keyboard, and a tiny 1 KB of RAM as standard. Its Z80 microprocessor was clocked at 3.25 MHz, and it had an 8 KB ROM, which included the BASIC language.
The ZX81 had two modes: FAST and SLOW. In SLOW mode, the video output worked normally, but the machine ran much slower. In FAST mode, the video output was only produced if the machine was waiting for user input — which tended to give a flickery display.
Dreams of Programming
Despite its limitations, the ZX81 was still a machine that I wanted to get my hands on. After using the Apple II and BBC Micro at school, I really wanted to experiment with programming at home — but all I had at the point was a programmable calculator.
Nearly a ZX81 Owner
In the end, I just missed out on having a ZX81 as my first computer. My high school computer studies teacher was selling one, but a classmate beat me to it. Looking back, I think the membrane keyboard and limited specification would have made it rather frustrating to use. I ended up with a Sinclair ZX Spectrum instead, which had colour and sound.
RAM Pack Wobble
My late wife owned a ZX81, with a 16 KB RAM expansion. She told me how she spent hours entering programs found in magazines, only to have the machine crash due to the dreaded ‘RAM pack wobble’, which was caused by the connection to the memory expansion being unreliable. When that happened, everything that had been typed in was lost. She also found the cassette interface to be unreliable for saving programs.
As with many other home computers, a wide range of extras appeared on the market for the ZX81. In addition to ordinary RAM expansions, I remember seeing one in the mid-80s which had 1 MB! Since the Z80 could only address a maximum of 64 KB, it would have involved a lot of paging. Maplin offered a range of add-ons for different computers. One of the things they sold for the ZX81 was a full-sized keyboard — and it was bigger than the ZX81 itself!
Several years ago, I was pleased to finally get my hands on a ZX81 — it was a gift from my wife. Despite being glad to have one, I have to admit that it’s not the nicest machine to use, and it doesn’t get powered up very frequently — it’s now more of an ornament.
Do you have memories of using the ZX81?
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